Fire detection in certain industries and especially in mining is known to be difficult due to the amount of dust and/or particulate matter suspended in the air. As such, traditional smoke detection devices cannot be used in such environments because the dust and/or suspended particulate matter is misinterpreted as smoke caused by a fire which often results in false alarms. Additional problems with such known detection devices include clogging of the detection devices with dust with that inhibits proper sensor function.
Known carbon monoxide sensors may be useful for detection of the combustion of certain materials, such as coal and wood. However, smoke monitoring remains necessary to detect fires with low heat and low output of carbon monoxide. For example, in many industries using heavy equipment, certain events may produce thick smoke while there is in fact no actual event that would result in the activation of a conventional temperature or carbon monoxide sensor and alarm. Moreover, certain gases are known to interfere with carbon monoxide sensors which limit or otherwise eliminate the use of such sensors in many applications.
Due to the limitations of the above devices, it is known to use optical obscuration smoke detectors in a particularly dusty or dirty environment where there may be smoke without heat or fire, such as an underground mine including coal mines. However, these reflected light-type devices are known to have difficulty correlating sensor output with the percent of obscuration of a light beam. For example, an amount of light reflected from smoke of a given light obscuration level may be dependent on the color of the smoke, particle size and distribution, degree of turbulence within the optical chamber of the device, etc. Therefore, it is difficult with known optical smoke detectors to make an accurate correlation of the amount of smoke and an actual fire, if not impossible.
U.S. Pat. No. 5,420,440 relates to an optical obscuration smoke detector that uses a horizontal air shunt to capture air flow. The downfall of this design is due to the reliance of the device on an environmentally dependent air flow (i.e., ambient air movement). The reliance on ambient air movement through the detection device in a location with low air flow, such as in a mine, may result in ineffective detection of smoke due to an inconsistent flow of air/smoke through its optical detector. Therefore, the device would have difficulty correlating sensor output with the percent of obscuration of a light beam.